A patent document 1 JP2005-351250, discloses a technique such that, in a hybrid vehicle including an engine and a first motor, both thereof being linked to driving wheels, and a second motor which is capable of generating an electric power using at least a part of a power from the engine, the first motor and second motor are drivingly controlled to modify an engine speed so as to cancel an influence when an air density is varied, thus an engine output being made substantially equal to a target value.
In addition, a patent document 2 JP2000-104590, discloses another technique such that, in the hybrid vehicle including a plurality of driving sources constituted by the engine and the motors, the motors controlling the driving force of the vehicle, and a transmission constituted by planetary gear sets, in a case where an output of the engine is reduced due to a variation in the atmospheric pressure and so forth and a vehicle torque that a vehicle driver intends is not achieved, the motors assist an insufficient part of the vehicle torque to obtain the vehicle torque that the driver intends.
However, since, in the hybrid vehicle disclosed in patent document 1, output torques of these first and second motors are not affected by the air density when the engine speed is modified by means of first and second motors so as to cancel the influence when the air density is varied, a stepwise difference in the driving force of the vehicle is developed when a driving state is transferred from a state in which the driving force of the vehicle is generated by the engine to a state in which the driving force of the vehicle is generated by the motor with the engine stopped and, consequently, there is a possibility that un unpleasant feeling is given to a vehicle driver.
In addition, in the hybrid vehicle described in patent document 2, such a problem that a consumed electrical power of a vehicle battery is increased when all of insufficient part of the output torque of the engine are tried to be compensated for by assistance torques of the motors is raised. In addition, in a case where the insufficient part of the output torque of the engine is assisted by the motors under a situation that each of the motors is generating the electric power, an electric power generation load of the motors is reduced so that there is a possibility that a sufficient electric power generation quantity cannot be secured any more.
Therefore, according to the present invention, in the hybrid vehicle having a first traveling mode in which the vehicle is driven utilizing the output of the engine and a second traveling mode in which the vehicle is driven through an output of the motor with the engine stopped, in a case where the air density is reduced with respect to a standard air density, the output of the motor in the second traveling mode is reduced with respect to the output of the motor in the standard air density.